The present invention relates to an apparatus and method for controlling an actuatable occupant restraint device for a vehicle. More particularly, the present invention relates to a method and apparatus for controlling an actuatable occupant restraint device having a velocity/displacement based threshold safing function with immunity box.
Actuatable occupant restraint systems, such as air bags, for vehicles are well known in the art. Such restraint systems include one or more collision sensing devices for sensing vehicle crash acceleration (vehicle deceleration). Air bag restraint systems further include an electrically actuatable igniter, referred to as a squib. When the collision sensing device senses a deployment crash event, an electrical current of sufficient magnitude and duration is passed through the squib to ignite the squib. When ignited, the squib initiates the flow of inflation fluid into an air bag from a source of inflation fluid, as is known in the art.
Certain known collision sensing devices used in actuatable occupant restraint systems are mechanical in nature. Still other known actuatable occupant restraint systems for vehicles include an electrical transducer, such as an accelerometer, for sensing vehicle crash acceleration. Systems using an accelerometer as a crash or collision sensor further include some circuitry, e.g., a controller, for monitoring the output of the accelerometer. The controller, such as a microcomputer, performs a crash algorithm on the acceleration signal for the purpose of discriminating between a deployment and a non-deployment crash event. When a deployment crash event is determined to be occurring, the restraint is actuated, e.g., an air bag is deployed.
One particular type of occupant restraint system known in the art is a multi-stage occupant restraint system includes more than one actuatable stage associated with a single air bag. In a multi-stage air bag restraint system, air bag inflation is the result of the control of a multi-stage inflator. Such multi-stage air bag systems typically have two or more separate sources of inflation fluid controlled by actuation of associated squibs. Known control arrangements control the actuation of the multiple stages based on a timer function. A problem arises in monitoring for a beginning of the crash event to start the timer. False starts (and endings) could occur due to signals resulting from road noise.
U.S. Pat. No. 3,966,224 is directed to a multi-stage air bag restraint system having two squibs. Under certain types of crash conditions, a first stage is actuated followed by actuation of a second stage a predetermined time after actuation of the first stage. If the crash acceleration is greater than a predetermined level, both stages are simultaneously actuated.
U.S. Pat. No. 4,021,057 is directed to a multi-stage air bag restraint system having a plurality of firing elements for gas generators. Crash velocity is compared against a plurality of threshold values for control of the plurality of squibs and, in turn, control of the inflation rate of the air bag.
U.S. Pat. No. 5,400,487 is directed to an air bag restraint system having a plurality of separately controlled gas generators actuated at selected times in a selected order to control the air bag""s inflation profile.
The selective triggering is a function of both the crash type extrapolated from past received acceleration data and the occupant position based on received occupant position data.
U.S. Pat. No. 5,411,289 is directed to an air bag restraint system having a multiple level gas generation source. xe2x80x9cThe electronic control unit is responsive to a combination of sensed inputs from the temperature sensor, the seat belt sensor, and the acceleration sensor for determining both an optimum gas generation level and inflation sequence times for controlling the multiple level gas generation source.xe2x80x9d (Abstract of ""289 patent)
Many types of crash algorithms for discriminating between deployment and non-deployment crash events are known in the art. Algorithms typically are adapted to detect particular types of crash events for particular vehicle platforms. One example of such an algorithm is taught in U.S. Pat. No. 5,587,906 to McIver et al. and assigned to TRW Inc.
Air bag restraint systems are also known to require more than one sensor for detection of a deployment crash event. Often, plural sensors are arranged in a voting scheme in which all the sensors must xe2x80x9cagreexe2x80x9d that a deployment crash event is occurring before restraint actuation is initiated. In certain known arrangements having a first and second sensor, the second sensor is referred to as a xe2x80x9csafing sensor.xe2x80x9d Air bag actuation occurs only if the first sensor and the safing sensor indicate a deployment crash event is occurring.
The present invention is directed to a safing apparatus for enabling and disabling an actuatable occupant restraint system. The apparatus includes means for determining whether a crash velocity value and a crash displacement value are within a threshold immunity box wherein the crash immunity box is defined by a crash velocity threshold value having a displacement based function and crash displacement threshold value.
In accordance with another aspect of the present invention, a method is provided for disabling and enabling an actuatable occupant restraint device comprising the steps of defining a threshold crash immunity box by a crash velocity threshold value having a displacement based function and a crash displacement threshold value, determining whether a crash velocity value and a crash displacement value are within the crash immunity box, and disabling and enabling the actuatable restraint device in response to the determination.